1. Field of the Invention
The present invention relates to insulation between coils of different phases of a stator of an electric motor and in particular to insulation of the coils at ends of the stator.
2. Description of Related Art
In manufacturing a stator of an electric motor, windings for respective phases are arranged along a plurality of slots formed on a stator core to form coils of respective phase with their edges projecting from respective ends of the slots. At intermediate portions of the coil edges projecting from the ends of the slots, insulation sheets of paper are intervened between coils of different phases for insulation thereof. In order to prevent lowering of the insulation by displacement of the insulation sheets, there have been proposed various improvements regarding shape of the insulation sheet, such as disclosed in JP 7-298530A.
Further, insulation at proximal portions of the coil edges is important as well as the insulation at the intermediate portions of the coil edges. As shown in FIG. 5, for the insulation at the proximal portions of the coil edges, an insulation sheet 20 in the form of a short strap, so-called as an angle sheet, has been used. As shown in FIG. 6, the angle sheet 20 is inserted into a slot 4 of a stator core 3 from which the coil 2 projects so as to insulate the coil 2 projecting from an end of the slot 4 of the stator core 3.
In the insulation of the coil edges of the stator, there are proposed various insulation methods for insulating the intermediate portions of the coil edges of different phases, but there is known only the method of insulation by means of the angle paper 20 with regard to the insulation at the proximal portions of the coil edges.
In the insulation method using the angle sheet 20, the angle sheet 20 in the form of the short strap is liable to displace when an external force is exerted in a direction along a short side of the strap. Thus, in the winding operation of the coils of the stator, after the windings are formed along the slots, the angle sheets 20 are inserted into the slots, and shapes of the coils are adjusted. The angle sheets 20 may displace, deform or slip off by movement of the coils in the adjusting operation to cause lowering of the insulation and necessity of rearrangement of the angle sheets 20. Further, since the angle sheet 20 is inserted into the slot from above, i.e., outside of the coil edges, it is liable that an amount of insertion of the angle sheet 20 is insufficient to make it difficult to securely fix the angle sheet 20 between a wall of the slot and the coil. Thus, the insulation at the proximal portion of the coil edges has been liable to be deteriorated for the above reasons.